Morphological features and elemental analysis of raw FA and prepared AC can be seen in the Figs. 1 and 2, respectively. Both figures contain SEM micrograph and associated EDS spectrum of raw oil FA (see Fig. 1) and AC (see Fig. 2). The investigation reveals that the raw ash particles are grey in color and of spherical shape with size ranging from few to several microns [27]. Pores are randomly located on the cenospheres and most of them are of macro range. Some spongy material also adheres to the ash particles which is also noticeable in the image. The EDS spectrum of raw material shows the high percentage of carbon with other metals like Mg, Ca, Fe, Cu, Ni, and Zn. These metals are present in form of oxides as indicated by the presence of oxygen [28]. Sulfur is present in a high percentage as compared with other metals. After implementing the activation procedure over raw ash all of the mineral metal contents have been removed [see Fig. 2(b)]. It seems elemental sulfur is bonded with carbon matrix that is why sulfur contents have also been reduced in the AC but not completely removed. The SEM images of AC [see Fig. 2(a)] reveal that the activation process generated meso and micro pores as a result of which surface area was increased manifold as compared with raw material. Few broken particles can also be seen in the SEM image which probably produced during thermochemical activation of raw ash.